Anaerobic digestion of brewing “waste”. L.S. Nkadimeng, S.T.L. Harrison Energy Postgraduate Conference 2013

Background Picture from : Effluents Beer Spent grain Spent yeast Wastewater University of Cape Town>> 18 September 2015 >> AD (wastewater treatment)

Anaerobic digestion (AD) Proteins Carbohydrates Lipids sugars Amino acids Fatty acids Organic acids, alcohols H 2, CO 2, NH 4 Acetate, H 2, CO 2 Biogas (CH 4, CO 2 ) Hydrolysis Acidogenesis Acetogenesis Methanogenesis t d : 30 minutes 1,4 to 5 days 2 to 3 days Boiler Water Steam to breweryCO 2 University of Cape Town>> 18 September 2015 >> (Mosey 1983; Lawrence & McCarty 1989; Gerber & Span 2008)

Spent grain Mechanical pre-treatment to promote hydrolysis: grinding Only 15% reduction in COD over 19 days of digestion Digestibility: (Aliyu & Bala, 2011, Mussatto & Teixeira, 2010) University of Cape Town>> 18 September 2015 >> - 4 -

Spent yeast: Effect of non-acclimated system on pH University of Cape Town>> 18 September 2015 >> - 5 -

Spent yeast: Slow incremental feeding University of Cape Town>> 18 September 2015 >> Highest removal rate: 962 mg-COD/L.day Removal efficiency: 69% in 1 day 97% in 3 days 99% in 9 days

Spent yeast: Continuous feed and draw University of Cape Town>> 18 September 2015 >> day HRT, SCOD/TCOD of feed ~ 60%

Spent yeast: Comparisons to SAB reactor University of Cape Town>> 18 September 2015 >> HRTAverage COD reduction rate COD reduction efficiency Substrate daysmg-COD/L.day Lab reactors %Spent yeast WTP at current op %Wastewater WTP design spec.1 (min) 4500 (max) -- Aim to reduce the HRT on lab reactors. Suggested strategies: recycling and continuous flow.

Degradation efficiency on spent grain was poor and not enhanced by mechanical pre-treatment. Spent grain is not viable as substrate in in the WTP. Acclimation of the system to yeast feed is important for auto-regulation of pH. Yeast is promising as substrate in the WTP. Future work Optimisation of yeast digestion on lab reactors. Anaerobic digestion experiment to mimic large scale digester (including biogas production measurements) Possibly, implementation of results on the WTP. Conclusions University of Cape Town>> 18 September 2015 >> - 9 -

Acknowledgements Prof. S T L Harrison University of Cape Town>> 18 September 2015 >>